Lightweight aircraft seal material

ABSTRACT

Disclosed herein is a novel approach to producing an aircraft window seal. The aircraft seal is produced of a much lighter material than has been used before, produced by a process of mixing a compound containing uncured silicone and a volume of microspheres, and then dispensing this material into a mold. Such a mold will normally be a female mold having the negative three dimensional shape of the aircraft seal to be produced. The seal may then be pressurized and/or heated during the curing process either prior to removing the seal from the mold or after removing the seal from the mold.

RELATED APPLICATIONS

This application claims priority benefit of U.S. Ser. No. 61/439,048,filed Feb. 3, 2011.

BACKGROUND OF THE DISCLOSURE

a) Field of the Disclosure

This application relates to the field of lightweight cabin, cockpit, andstorage window and door seals for commercial, personal, military, andother aircraft.

b) Background Art

Malleable seals for aircraft have been in use since aircraft first usedwindows. Such seals are similar in some respects to the malleable sealsfound in homes, automobiles, boats, and elsewhere. Generally, such sealsform a weather-tight malleable separation between the outer hull (frameand skin) of the aircraft and the window(s). Such seals are utilized sothat the interior of the cabin stays warm, dry, and in modern aircraft,pressurized. Such seals must remain useable in the presence of very highpressures differentials between the interior and exterior of aircraftthat fly at high altitudes. Such pressures are utilized to supplysufficient oxygen (and heat) to passengers and crew.

FIG. 1 shows a highly schematic view of a modern aircraft windowassembly 20 in cross section. The aircraft skin and frame are shown at22 with an outer transparent window pane 24 and inner transparent windowpane 26 separated by an airspace 28. The use of double panes is a commonstructure which improves thermal and acoustic insulation of theassembly, and in some applications allows for air to be evacuated fromthe airspace 28 to reduce condensation, improve thermal and acousticinsulation, and improve visual transmission through the window assembly.

Especially as fuel costs rise, aircraft manufacturers and airlines arelooking to reduce the weight of the aircraft and load in any waypossible. Airlines have in some applications removed magazine racks,redesigned food and beverage carts, used lighter frame materials such ascarbon fiber over the much heavier traditional aluminum, reduced theallowed baggage each passenger is allowed to bring without additionalcost to them, etc.

As the limits of weight reduction infringe on safety issues, reducingthe weight of the aircraft and load becomes exponentially moredifficult.

SUMMARY OF THE DISCLOSURE

Disclosed herein is a lightweight aircraft window seal made by the stepscomprising: providing a volume of viscoelastic fluid silicone; providinga volume of microspheres; combining the fluid silicone with themicrospheres to produce a lightweight fluid. The lightweight fluid isthen disposed into a female mold having the negative three dimensionalshape of the aircraft seal. The lightweight fluid is then allowed tocure; and is removed from the mold.

To promote a better seal in one embodiment, the process for forming theaircraft window seal as recited above may further comprise the step ofapplying heat to the lightweight fluid during the curing process. Thisstep of applying heat to the lightweight fluid may be enacted during thecuring process prior to removing the seal from the mold.

While the aircraft window seal as recited above may utilize severaldifferent microspheres, in one embodiment the microspheres are airfilled glass spheres. These air filled glass spheres in one embodimentmay be formed of silica quartz, although other materials may also beutilized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a highly schematic view of an aircraft window seal in crosssection, produced by one embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As stated previously, reduction of the overall weight of an aircraft andload (including passengers, crew, baggage, freight, etc.) has been apriority for aircraft designers, manufacturers, and airlines for sometime. The limits of such weight reduction however have an upper limit.As obviously superfluous items are removed, removal of the remainingitems may not be practical. As the lightest known materials andcomposites are then used for the remaining items such as windows,frames, seats, etc. are used, additional weight reduction becomes muchmore difficult.

In this endeavor to lighten the aircraft without sacrificing structuralintegrity, the malleable seals used to seal the windows and doors to theframe and/or skin of the aircraft were examined to determine if there isa potential to reduce the weight thereof without sacrificing structuralintegrity of the seal or surrounding structure. While this may not seemto have a significant impact on the weight of the aircraft, it should benoted that modern aircraft may have 200 passenger windows or more. Manyaircraft manufacturers and their customers are looking at ways to makethe traditional aircraft windows larger to increase outside visibilityand reduce the amount of power required for interior lighting. Inaddition, the door seals, hatch seals, windshield seals, and othercomponents may also be converted from the rubber, silicone, or otherrelatively heavy materials to the disclosed material, further decreasingthe overall weight of the aircraft.

While the term “window seals” is used herein for brevity, the disclosedmaterial may also be used in malleable door seals, hatch seals, andother equivalent components which are positioned between separate rigidstructures.

Disclosed herein is a novel approach to producing an aircraft windowseal produced of a much lighter material than has been used before. Theaircraft window seal is produced by mixing a compound containing uncuredsilicone and a volume of microspheres, and then dispensing this materialinto a mold. Such a mold will normally be a female mold having thenegative three dimensional shape of the aircraft seal to be produced.The seal may then be pressurized and/or heated during the curing processeither prior to removing the seal from the mold, or after removing theseal from the mold.

This approach is effective as the microspheres are less dense than thesilicone or rubber traditionally used. Microspheres themselves are noteffective as seals for many reasons including their lack ofmalleability, airflow around adjacent microspheres, and potentiallyairflow through individual microspheres. In addition, while asignificant percentage of the material needs to be made of microspheresin order to establish a weight loss of the final composition, a delicatebalance must be achieved in each application between the volume ofsilicone, and the volume of microspheres. Using to high a percentagevolume of microspheres would result in a poor material due to lack ofmalleability, and possibly airflow through the material. As the windowstend to deflect outward as the aircraft is pressurized from within,especially at cruising altitudes, such malleability is especiallyimportant to maintain integrity of the seal. It is also suspected that ahigh percentage of microspheres may adversely effect the migration ofthe seal relative to the window and/or aircraft frame/skin.

The term microspheres is a term well known in the art as nearlymicroscopic spheres typically (typically 1 μm to 1000 μm (1 mm)),commonly made of glass (quartz) or other ceramics. The spheres arecommonly hollow and air-filled, but may be filled with other gasses andmay not be sealed (open cell) hollow spheres. Microspheres are alsocommonly polyethylene and polystyrene.

Such a seal for aircraft as recited above is particularly well suitedfor any commercial or military aircraft where weight savings aredesirable in order to increase fuel efficiency.

The disclosed lightweight viscoelastic fluid has been produced andtested by combining a volume of fluid silicone with a volume of microspheres. The test results of a gasket made from this material are shownbelow:

Test method Results Durometer Points ATSM D 2240 55 Tensile StrengthPSI, Min ATSM D 412 682 Elongation % Min ATSM D 412 520 Tear ResistancePPI, Min ATSM D 624 80 Specific Gravity Points ATSM D 297 1.00

The seal comprises a seal gasket made from a formulated compoundcontaining viscoelastic fluid silicone and micro spheres.

Viscoelasticity is the property of materials that exhibit both viscousand elastic characteristics when undergoing deformation. Viscousmaterials, like honey, resist shear flow and strain linearly with timewhen a stress is applied.

The uncured compound may be injected, poured, or placed by hand in themold. The mold is then closed and compound is allowed to cure for a timewhereupon the mold is opened and the finished part (seal) is removed. Insome applications, the uncured compound may be subjected to heat and orpressure to effect physical and/or chemical changes in the material. Forexample, the uncured compound may be injected into the mold, whereuponthe mold and material are subjected to increased pressures and increasedtemperatures during at least part of the curing process.

It may also be desired to increase production output, to remove thepartially cured seal from the mold. The partially cured seal may besubjected to heat, pressure, or may just be allowed to cure over timeoutside of the mold. As long as the uncured seal holds the desired shapeuntil completely cured, it may not be detrimental to remove it from themold prior to final curing.

The seal may then be installed into an aircraft to hold windows in placeand seal the gap between the window and the aircraft frame or skin.

While the present invention is illustrated by description of severalembodiments and while the illustrative embodiments are described indetail, it is not the intention of the applicants to restrict or in anyway limit the scope of the appended claims to such detail. Additionaladvantages and modifications within the scope of the appended claimswill readily appear to those sufficed in the art. The invention in itsbroader aspects is therefore not limited to the specific details,representative apparatus and methods, and illustrative examples shownand described. Accordingly, departures may be made from such detailswithout departing from the spirit or scope of applicants' generalconcept.

Therefore we claim:
 1. A method for making a lightweight aircraft windowseal comprising the steps of: providing a volume of viscoelasticsilicone; providing a volume of microspheres; combining the viscoelasticsilicone with the microspheres to produce a lightweight viscoelasticcompound; disposing the lightweight viscoelastic compound into a femalemold having the negative three dimensional shape of the aircraft seal;subjecting the viscoelastic compound to increased pressure and heat overtime to cure forming the aircraft window seal; removing the aircraftwindow seal from the mold applying the cured window seal to an aircraftwindow; and applying the window seal-window combination to an aircraftto seal a gap between the window and the aircraft.
 2. The method formaking an aircraft window seal as recited in claim 1 wherein themicrospheres are air filled glass spheres.
 3. The method for making anaircraft window seal as recited in claim 2 wherein the air filled glassspheres are formed of silica quartz.
 4. The method for making anaircraft window seal as recited in claim 1 wherein the step of disposingthe lightweight viscoelastic compound into a female mold is accomplishedby pressure injection molding.